Poly-V pulley made of metal sheet and method of manufacturing the same

ABSTRACT

The present invention relates to a cylindrical poly-V pulley made of metal sheet suitable for forcedly fitting a one-way clutch or a bearing. The present invention can easily provide thick ears for preventing a V-belt from disengaging, and ensure an enough length of an axial straight line of a bore of a peripheral wall. Ears ( 2, 2 ) for preventing the V-belt from disengaging, are protrusively shaped in an annular state on axially both ends on an outer surface of a cylindrical peripheral wall ( 1 ). The each ear ( 2 ) includes an inner ear portion ( 2   a ) outwardly protruded from the both ends of the peripheral wall ( 1 ) and an outer ear portion ( 2   b ) folded back from the protruded outer end of the inner ear portion ( 2   a ) to the outer surface of the inner ear portion ( 2   a ) so as to be closely overlapped with each other, and the inner end surface of the ear ( 2 ) is flush with the inner surface of the peripheral wall ( 1 ). Therefore, the ear ( 2 ) can be thickened by an overlap structure by the inner and outer ear portions ( 2   a ) and ( 2   b ), and the length of the axial straight line of the bore of the peripheral wall ( 1 ) can be ensured for the thickness of the outer ear portion ( 2   b ).

TECHNICAL FIELD

[0001] The present invention relates to a poly-V pulley made of metalsheet used together with a V-belt for transmitting a rotational powerand a method of manufacturing the same.

BACKGROUND ART

[0002] As a poly-V pulley of this kind, for the usage purpose ofinsertion and coupling onto a shaft via a one-way clutch or a bearing,known is a poly-V pulley of a structure in which a cylindricalperipheral wall is formed, an ear for preventing a V belt fromdisengaging is outwardly and protrusively formed in each of the axialends of the outer peripheral face of the peripheral wall, and poly-Vgrooves are formed between the both ears.

[0003] Generally, such a poly-V pulley is made of cast iron. However,the poly-V pulleymade of cast iron is heavy. Moreover, the poly-Vgrooves are formed by cutting operations, thereby causing a problem ofscattering many cut powders in workshops and worsening workingenvironment. On the other hand, the poly-V pulley made of metal sheet,which is made of a flat plate material such as a rolled steel, hasadvantages: it is more durable, more lightweight and cheaper than thepoly-V pulley made of cast iron.

[0004] The poly-V pulley made of metal sheet is disclosed in a gazetteof Japanese Patent Laying-open No. 8-300082. The disclosed poly-V pulleyhas steps wherein, preparatory to forming ears for preventing a V belt(called as a belt guide in the gazette) from disengaging, on the axiallyboth ends of a peripheral wall portion, preliminary ears (called as aportion where a guide is formed in the gazette) are formed on the bothends of the cylindrical peripheral wall by means of press process andsplitting process, and the each preliminary ear whose structure is asingle layer having a predetermined shape is subsequently shaped in thefollowing step.

[0005] However, the ear having a single layer is thin so that mechanicalstrength thereof is inferior. In order to obtain the ear having anenough rigidity and an enough protrusive length, a thick blank isrequired. However, it is not easy to draw a thick blank so as to becomea cup-shape with a bottom surface.

[0006] Then, an object of the present invention is to provide a poly-Vpulley made of metal sheet having a superior rigidity, which makes itpossible to obtain easily thick ears from the flat plate material whosethickness is not so great and which is easily drawn, and to ensure thelength of the axial straight line of a bore of the cylindricalperipheral wall suitable for forcedly inserting the one-way clutch andthe bearing, and a method of manufacturing the same.

DISCLOSURE OF THE INVENTION

[0007] A poly-V pulley made of metal sheet according to the presentinvention comprises:

[0008] a cylindrical peripheral wall,

[0009] annular ears for preventing a V belt from disengaging, the earsbeing protrusively formed in axially both ends of an outer surface ofthe peripheral wall, and

[0010] poly-V grooves disposed between the both ears on the outersurface of the peripheral wall,

[0011] wherein at least one of the both ears includes an inner earportion protruded from the end of the peripheral wall to the outwarddirection, and an outer ear portion folded back from the protruded outerend of the inner ear portion to an outer surface of the inner earportion, so as to be closely fitted therewith, and the inner end surfaceof the ear is formed to be flush with the inner surface of theperipheral wall.

[0012] According to the poly-V pulley made of metal sheet, the inner andouter ear portions are folded to overlap with each other, therebyensuring enough thickness of the ears so as to increase the rigidity,and making it possible to increase the length of the axial straight lineof a bore of the peripheral wall only for a thickness of the outer earportion. This can enough ensure an effective contact supporting surfacewith the outer surface of the one-way clutch or the bearing which areforcedly fit into the inner surface of the peripheral wall.

[0013] In case that the each ear on the both ends thereof has asectional structure wherein the inner and outer ear portions are foldedso as to be overlapped with each other, its rigidity is more enhancedthan that of a case that only one ear has such a sectional structure.Therefore, the inner surface of the peripheral wall is finished bymachining work so as to have a predetermined inside diametermeasurements and become completely circular, thereby making it possibleto finish accurately it so as to be suitable for forcedly fitting aone-way clutch, a bearing or the like.

[0014] A method of manufacturing a poly-V pulley made of metal sheethaving the above structure, according to the present invention,comprises the steps of:

[0015] forming a cup-shaped forming body which has a bulging middleportion-peripheral wall like a barrel, integrated with an outerperiphery of a circular bottom wall;

[0016] preparing a roller for forming ears provided with a concaveforming surface and an annular projection, the concave forming surfacewhich is concavely arc-shaped being disposed on an axial center portionof the outer surface, and the annular projection whose section isV-shaped being disposed on axially both ends of the concave formingsurface;

[0017] applying a compressive load to the cup-shaped forming body in theaxial direction at the same time while pressing the annular projectionof the roller for forming ears against the outer surface of the bulgingmiddle portion-peripheral wall in a radially inward direction thereof,

[0018] folding at least axial one end of the bulging middleportion-peripheral wall into two, and

[0019] protrusively forming inner and outer ear portions overlapped soas to be closely fitted with each other;

[0020] pressing a straightening roller having a shaping surfaceperpendicular to the outer periphery of the bulging middleportion-peripheral wall, against the outer surface of the bulging middleportion-peripheral wall in the radially inward direction thereof,

[0021] straightening the bulging middle portion-peripheral wall so as tobe parallel with the axial direction, and

[0022] forming the perpendicular peripheral wall;

[0023] shaping the each poly-V groove between the ears on the outersurface of the perpendicular peripheral wall by means of rolling;

[0024] shearing a connecting portion between the bottom wall of theperpendicular peripheral wall and the ear, so as to remove the bottomwall; and

[0025] finally performing a machining work so as to make the inner endsurface of the ear flush with the inner surface of the perpendicularperipheral wall.

[0026] According to such a manufacturing method, the compressive load isaxially applied to the bulging middle portion-peripheral wall of thecup-shaped forming body, while the annular projections of the roller forforming ears are radially pressed against it. This can facilitatefolding at least one end of the bulging middle portion-peripheral wallso as to closely fit the inner ear portion with the outer ear portionand be overlapped.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a sectional view of an embodiment of a poly-V pulleymade of metal sheet according to the present invention.

[0028]FIG. 2 is a diagram of a first step in manufacturing the poly-Vpulley made of metal sheet according to the present invention.

[0029]FIG. 3 is a diagram of a second step in manufacturing the same.

[0030]FIG. 4 is a diagram of a third step in manufacturing the same.

[0031]FIGS. 5A and 5B are diagrams respectively showing a fourth stepfor manufacturing the same.

[0032]FIGS. 6A and 6B are diagrams respectively showing a fifth step formanufacturing the same.

[0033]FIGS. 7A, 7B and 7C are diagrams respectively showing a sixth stepfor manufacturing the same.

[0034]FIG. 8 is a diagram of a seventh step for manufacturing the same.

[0035]FIG. 9 is a diagram of an eighth step in manufacturing the same.

[0036]FIG. 10 is a diagram of a ninth step in manufacturing the same.

[0037]FIG. 11 is a sectional view of another embodiment of the poly-Vpulley made of metal sheet according to the present invention.

[0038]FIG. 12 is a diagram of one step in manufacturing the poly-Vpulley made of metal sheet shown in FIG. 11.

BEST MODES FOR CARRYING OUT THE INVENTION

[0039] An embodiment of a poly-V pulley made of metal sheet according tothe present invention will be described with reference to the drawings.

[0040]FIG. 1 is a sectional view of a poly-V pulley made of metal sheet,manufactured by the embodiment of the present invention. The poly-Vpulley made of metal sheet comprises a cylindrical peripheral wall 1,annular ears 2 protrusively formed from axial both ends on an outersurface of the cylindrical wall 1 to an outward direction, and poly-Vgrooves 4 formed between the ears 2, 2 on the outer surface of the body1. The poly-V pulley made of metal sheet, for example, is inserted in ashaft for transmitting motive power via a one-way clutch or a bearing soas to join them. The ears 2, 2 are preventive walls for preventing apoly-V belt from accidentally going over the poly-V grooves 4 under thecondition wherein the poly-V belt hangs on the poly-V grooves 4.

[0041] The each of ears 2, 2 includes an inner ear portion 2 a and anouter ear portion 2 b. The inner ear portion 2 a is protruded from theaxial both ends of the peripheral wall 1 to the outside. The outer earportion 2 b is folded back from the protruded outer end of the inner earportion 2 a to the outer surface of the inner ear portion 2 a, so as tomake them closely fitted. An inner end surface 2 c of the ear 2 isformed to be flush with an inner surface 1 a of the peripheral wall 1.

[0042] The ear 2 has a double section structure wherein the inner andouter ear portions 2 a and 2 b are folded, thereby enhancing rigiditybetween the each ear 2 and the both ends of the peripheral wall 1.Moreover, a length of an axial straight line of the inward radialportion of the peripheral wall 1 can be more increased only for athickness of the outer ear portion 2 b in comparison with a single layerwherein the ear 2 comprises only an inner ear portion 2 a, therebyensuring a larger contact surface between the outer surface of theone-way clutch or the bearing which is forcedly inserted into a bore ofthe peripheral wall 1 and the inner surface 1 a of the peripheral wall1.

[0043] Next, the embodiment of a method of manufacturing a poly-V pulleymade of metal sheet according to the present invention will be describedwith reference to FIGS. 2 to 10.

[0044]FIG. 2 shows a first step. In the first step, a metal flat platematerial such as a rolled steel is circularly punched, thereby obtaininga blank. The blank is drawn so as to form a cup-shaped forming body 10.In the step, the blank is drawn and shaped by upper and lower dies 11and 12, thereby obtaining the cup-shaped forming body 10 including aflat bottom wall 13, a peripheral wall forming portion 14 connectedly tothe outer periphery of the bottom wall 13, and a protruded edge 14 aprotruded in a widening state from an open-side end of the peripheralwall forming portion 14 to the slightly outward direction.

[0045]FIG. 3 shows a second step. In this step, upper and lower dies 15and 16 are used. The upper die 15 is provided with a recessed portion 18for shaping a bulging portion. The lower die 16 is provided with aprotruded portion 19 for shaping a bulging portion. Between the upperand lower dies 15 and 16, the cup-shaped forming body 10 obtained by thefirst step is clamped, so as to draw a bulging portion 17 on the centerof the bottom wall 13 thereof, thereby obtaining a cup-shaped formingbody 20.

[0046]FIG. 4 shows a third step. The step is a trimming step forobtaining a cup-shaped forming body 21. In other words, the protrudededge 14 a of the peripheral wall forming portion 14 of the cup-shapedforming body 20 obtained by the second step is cut so as to leave onlythe peripheral wall forming portion 14 with a uniform thickness.

[0047]FIGS. 5A and 5B show a fourth step. FIG. 5A shows a state previousto applying a process. FIG. 5B shows a state after applying a process.In the fourth step, as shown in FIG. 5A, a lower die 23 is prepared,which has a recessed portion 22 to fit an outer shape of the bottom wall13 of the cup-shaped forming body 21 obtained by the third step. Thecup-shaped forming body 21 is set on the recessed portion 22 of thelower die 23 so that an opening mouth may be directed upward. As shownin FIG. 5B, an upper die 25 which has a recessed portion 24 with a roundcorner portion 24 a, is lowered so that an open edge 14 b of theperipheral wall forming portion 14 is inwardly bent at the round cornerportions 24 a of the recessed portion 24, thereby obtaining a cup-shapedforming body 26. The fourth step is a step for facilitating bulging ofthe peripheral wall forming portion 14 like a barrel in a fifth step forbulging.

[0048]FIGS. 6A and 6B show the fifth step. FIGS. 6A and 6B showrespectively a state previous to applying a process, and a state afterapplying the process. In the fifth step, as shown in FIG. 6A, upper andlower dies 28 and 30 are used. The upper die 28 has a recessed portion27 to fit an outer shape of the bottom wall 13 of the cup-shaped formingbody 26 obtained by the fourth step, and a lower die 30 has an annulargroove 29 which can be loosely fitted to the open edge 14 b curved to aninside of the peripheral wall forming portion 14 of the cup-shapedforming body 26. The open edge 14 b curved to the inside of theperipheral wall forming portion 14 of the cup-shaped forming body 26 isloosely fitted to the annular groove 29 of the lower die 30. The bottomwall 13 of the cup-shaped forming body 26 is fitted to the recessedportion 27 of the upper die 28. Then, as shown in FIG. 6B, the upper die28 is lowered thereby buckling the cup-shaped forming body 26 by meansof an axial load. As a result, the peripheral wall forming portion 14 isbulged in a barrel state, thereby obtaining a cup-shaped forming body 32which is provided with a bulging middle portion-peripheral wall 31.

[0049]FIGS. 7A, 7B and 7C show a sixth step. FIG. 7A shows a stateprevious to applying a process, and FIGS. 7B and 7C show a state afterapplying the process. In the sixth step, as shown in FIG. 7A, upper andlower dies 34 and 40, a roller 43 for forming ears, and a straighteningroller are prepared. The upper die 34 is provided with a recessedportion 33 which fits the outer shape of the bulging portion 17 of thebottom wall 13 of the cup-shaped forming body 32 obtained by the fifthstep. The lower die 40 is provided with a protruded portion 37 includingan upper end portion 35 and a vertical peripheral surface 36, and anannular groove 38 formed at a root portion of the protruded portion 37.The roller 43 for forming ears (whose sectional views are shown in FIGS.7A, 7B and 7C) includes a concave forming surface 41 which is concavelyarc-shaped, formed on the axial center of the outer surface, andV-shaped annular projections 42, 42 on the axially both ends of theconcave forming surface 41. The straightening roller 45 is provided witha forming surface 44 vertical to the outer surface of the bulging middleportion-peripheral wall. As shown in FIG. 7A, the outer periphery of theprotruded portion 37 of the lower die 40 is covered with the cup-shapedforming body 32 obtained by the fifth step, in a loosely fitted state,and a curved opening end 31 a of the bulging middle portion-peripheralwall 31 is engaged with the annular groove 38. With respect to the upperdie 34, the bulging portion 17 of the bottom wall 13 of the cup-shapedforming body 32 is engaged with the recessed portion 33 of the upper die34. In the setting state, the upper die 34 is initially lowered as shownin FIG. 7B. A compressive load is axially applied to the cup-shapedforming body 32, so that an inside of the bulging portion 17 of thecup-shaped forming body 32 may be engaged with the upper portion of thelower die 40, thereby rotating the upper and lower dies 34, 40 aroundO₁. Moreover, the annular projections 42, 42 of the roller 43 forforming ears are pressed in a radially inward direction thereof againstthe outer surface of the bulging middle portion-peripheral wall 31, atthe same time while the roller 43 for forming ears is rotated around O₂.As a result, the axially both ends of the bulging middleportion-peripheral wall 31 are folded in a double state so as to beoverlapped and closely fitted with each other, thereby protrusivelyforming the ears 2 including the inner and outer ear portions 2 a, 2 b.In this case, the annular projections 42, 42 of the roller 43 forforming ears are radially pressed against the bulging middleportion-peripheral wall 31 of the cup-shaped forming body 32, while thecompressive load is axially applied thereto, thereby making it easy tofold and shape the inner and outer ear portions 2 a, 2 b.

[0050] Furthermore, as shown in FIG. 7C, the upper and lower dies 34, 40are rotated around O₁, and the vertical forming surface 44 of thestraightening roller 45 is pressed in a radially inward directionagainst a portion between the ears 2, 2 on the both ends of the outersurface of the bulging middle portion-peripheral wall 31, while thestraitening roller 45 is rotated around O₃, and the bulging middleportion-peripheral wall 31 is axially straightened, thereby obtainingthe cup-shaped forming body 47 whose peripheral wall 46 has been shapedto be vertical.

[0051]FIG. 8 shows a seventh step. In this step, upper and lower dies50, 54, and a rolling roller 55 (shown in a sectional view in FIG. 8)are prepared. The upper die 50 includes a protruded portion 48 whichfits a shape of the inside of the cup-shaped forming body 47 obtained bythe sixth step, and an annular groove 49 formed on a root portion of theprotruded portion 48. The lower die 54 includes a recessed portion 51which fits an outer shape of the bottom wall 13 of the cup-shapedforming body 47, and an annular groove 53 formed on an outer peripheryof the annular projection 52 of an outer periphery of the recessedportion 51. In this step, the cup-shaped forming body 47 obtained by thesixth step is vertically reversed, the bottom wall 13 is engaged withthe recessed portion 51 of the lower die 54, and the ear 2 of the bottomwall 13 is engaged with the annular groove 53 of the lower die 54. Then,the upper die 50 is lowered, the protruded portion 48 is engaged withthe inside of the cup-shaped forming body 47, and the ear 2 on a side ofthe opening end of the peripheral wall 46 is engaged with the annulargroove 49. The cup-shaped forming body 47 is clamped between the upperand lower dies 50 and 54, thereby enhancing degree of overlap-fitting ofthe overlapped ears 2, 2 which has a double structure (especially,degree of overlap-fitting of the ear 2 on a side of the opening end,which is apt to be slightly loosened).

[0052] Moreover, in the step of enhancing the degree of overlap-fittingof the ears 2, 2, the upper and lower dies 50, 54 are rotated around O₄,and the rolling roller 55 for preliminary shaping poly-V grooves ispressed in a radially inward direction against the outer periphery ofthe peripheral wall 46, while the rolling roller 55 is rotated aroundO₅. As a result, a cup-shaped forming body 56 may be obtained, which hasbeen subjected to preliminary shaping of the poly-V grooves between theears 2, 2 on the outer surface of the peripheral wall 46.

[0053]FIG. 9 shows a eighth step. In this step, the cup-shaped formingbody 56 obtained by the seventh step is clamped between the upper andlower dies 57 and 58, so as to be rotate around O₆. Against the portionbetween the ears 2, 2 on the outer surface of the peripheral wall 46 ofthe cup-shaped forming body 56, a groove 59 a of an outer periphery of arolling roller 59 (shown in a sectional view in FIG. 9) is stronglypressed in a radially inward direction thereof, while the rolling roller59 is rotated around O₇, thereby shaping the poly-V grooves 4 as pluralV groove-groups between the ears 2, 2 on the outer surface of theperipheral wall 46. Consequently, a cup-shaped forming body 62 isobtained. Though the process for shaping the poly-V grooves 4 may beperformed by once rolling operation, it is more preferable that a numberof rolling operations are repeatedly performed, thereby finishing thepoly-V grooves so as to have a depth and a pitch as a final shapethereof.

[0054]FIG. 10 shows a ninth step. In this step, the bottom wall 13 ofthe cup-shaped forming body 62 obtained by the eighth step is clampedbetween an upper die 60 and a lower die 61. A movable blade 63 forshearing, which is vertically movable, is arranged on the outerperiphery of the upper die 60. The movable blade 63 is lowered, therebyshearing a connecting portion C between the bottom wall 13 and the ear 2with the result that the bottom wall 13 is pulled out. The connectingportion C is an area on the axial extending line of the inner surface ofthe peripheral wall 46.

[0055] The last step, namely, a tenth step provides a poly-V pulley madeof metal sheet as shown in FIG. 1 in a following manner. The innersurface of the cylindrical peripheral wall 46 obtained by the ninth stepand the inner end surface 2 c of the ear 2 are finished by machiningwork so as to be flush with each other. In the case of machining work,there are the very thick ears 2, 2 doubly folded on the both ends of theperipheral wall 46, and the rigidity of the both ends of the peripheralwall 46 is great. Therefore, inward diameter measurements andcircularity of the peripheral wall 46 can be accurately finished.Moreover, even after performing the finishing work, a distortion israrely caused in a bore of the peripheral wall 46, thereby ensuringcircularity.

[0056] As shown in the above embodiment, it is the most preferable thatthe ears 2,2 on the both ends of the peripheral wall 46 of the poly-Vpulley made of metal sheet are respectively formed as multiple layersincluding the inner and outer ear portions 2 a, 2 b. However, it may notbe limited to the structure. As shown in FIG. 11, it is also allowedthat only one ear 2 is formed as multiple layers including the inner andouter ear portions 2 a, 2 b, and the other ear 2 is a single layer. Inthis case, for example, in the sixth step of FIG. 7B of the embodiment,the roller 43 for forming ears shown in FIG. 12 is used, whose oneannular projection 42 is formed into a sharpened edge blade 62. In thesixth step, an area which the bottom wall 13 intersects the peripheralwall 31, is subjected to splitting process by the sharpened edge blade62, whereby the ear 2 as the single layer may be formed. The ear 2 asthe multiple layers including the inner and outer ear portions 2 a, 2 bis formed by the other annular projection 42 of the roller 43 forforming ears in the same way as the above embodiment. Except it, thefirst to fifth steps and the seventh to tenth steps are performed in thesame way as the above embodiment.

[0057] Industrial Applicability

[0058] According to the present invention, at least one of the ears onboth ends of the peripheral wall of the poly-V pulley made of metalsheet, comprises the inner and outer ear portions doubly folded, therebymaking it easy to obtain the thick ear from a flat plate material whichis not so thick and easy to be drawn. Moreover, this ensures the enoughlength of the axial straight line of the bore of the peripheral portion.Consequently, the cylindrical poly-V pulley made of metal sheet, whichis suitable for forcedly fitting one-way clutch and a bearing, can beeasily and economically produced.

1. A poly-V pulley made of metal sheet comprising: a cylindricalperipheral wall, annular ears for preventing a V belt from disengaging,the ears being protrusively formed in axially both ends of an outersurface of the peripheral wall, and poly-V grooves disposed between theboth ears on the outer surface of the peripheral wall, wherein at leastone of the both ears includes an inner ear portion protruded from theend of the peripheral wall to the outward direction, and an outer earportion folded back from the protruded outer end of the inner earportion to an outer surface of the inner ear portion, so as to beclosely fitted therewith, and the inner end surface of the ear is formedto be flush with the inner surface of the peripheral wall.
 2. A methodof manufacturing a poly-V pulley made of metal sheet, the poly-V pulleymade of metal sheet comprising: a cylindrical peripheral wall, annularears for preventing a V belt from disengaging, the ears beingprotrusively formed in axially both ends of an outer surface of theperipheral wall, and poly-V grooves disposed between the both ears onthe outer surface of the peripheral wall, wherein at least one of theboth ears includes an inner ear portion protruded from the end of theperipheral wall to the outward direction, and an outer ear portionfolded back from the protruded outer end of the inner ear portion to anouter surface of the inner ear portion, so as to be closely fittedtherewith, and the inner end surface of the ear is formed to be flushwith the inner surface of the peripheral wall, comprising the steps of:forming a cup-shaped forming body which has a bulging middleportion-peripheral wall like a barrel, integrated with an outerperiphery of a circular bottom wall; preparing a roller for forming earsprovided with a concave forming surface and an annular projection, theconcave forming surface which is concavely arc-shaped being disposed onan axial center portion of the outer surface, and the annular projectionwhose section is V-shaped being disposed on axially both ends of theconcave forming surface; applying a compressive load to the cup-shapedforming body in the axial direction at the same time while pressing theannular projection of the roller for forming ears against the outersurface of the bulging middle portion-peripheral wall in a radiallyinward direction thereof, folding at least axial one end of the bulgingmiddle portion-peripheral wall into two, and protrusively forming innerand outer ear portions overlapped so as to be closely fitted with eachother; pressing a straightening roller having a shaping surfaceperpendicular to the outer periphery of the bulging middleportion-peripheral wall, against the outer surface of the bulging middleportion-peripheral wall in the radially inward direction thereof,straightening the bulging middle portion-peripheral wall so as to beparallel with the axial direction, and forming the perpendicularperipheral wall; shaping the each poly-V groove between the ears on theouter surface of the perpendicular peripheral wall by means of rolling;shearing a connecting portion between the bottom wall of theperpendicular peripheral wall and the ear, so as to remove the bottomwall; and finally performing a machining work so as to make the innerend surface of the ear flush with the inner surface of the perpendicularperipheral wall.